Differential gearing and power transmission



Nov. 26, 1935. I P. s. MORGAN DIFFERENTIAL GEARING AND POWER TRANSMISSION Filed Nov. 22, 1953 s Sheets-Sheet 1 I ditome'g 4 Nova 26, M35 s. MORGAN DIFFERENTIAL GEARING AND POWER TRANSMISSION Filed Nov. 22', 1955 s Sheets-Sheet 2 |||||||||||fl|M||||||H| lllWmml...... iiiiiiiiiiiiiiiiliiiiiiliilnlnlulmlmlllllmill am/e A TTO EYS.

adapted to Patented Nov. 26, v1935 UNITED STATES DIFFERENTIAL GEARING POWER- TRANSMISSION Porter S. Morgan,

one-tenth to Albert R. Henry,

New York, N. Y., asslgnor of Buffalo, N. Y.

- Application November 22, 1933, Serial No. 699,154 8 Claims. (01. 'l43 13) This invention relates to differential gearing and power transmission, and it has particular reference to a system of power transmission. from a main drive shaft to a plurality of driven shafts rotate at varying speeds and subject to varying resistances wherein power is effectively transmitted to the driven shaft encountering the greater resistance, and the invention also relates to a worm gearing by means of which the stated power transmission and differential action may be obtained in a simple, inexpensive, and eflicient manner.

It is' frequently desirable to transmit power from a driving member to one or more driven shafts under conditions permitting such shafts torotate at different speeds at different times. Gearing intended to produce this result is called differential gearing, and, while various forms of gears have been'proposed in such systems, the

most common form is that employing planetary bevel gears, such as are used in the transmission of power to the rear wheels of an automobile. It is an inherent characteristic of such gearing that the power is not delivered at all times to' the driven shafts in proportion to the loads imposed thereon, but rather, it is frequently delivered in inverse ratio thereto. For a common exanzple, reference maybe made to the conditions encountered in an automobile when one wheel is free from the ground, or is resting on ice or: in mud or other slippery surface. Under these conditions, the power is transmitted to the wheel encountering the less resistance, and there is little, if any, effective power transmitted for 'the purpose of moving the vehicle.

While this inherent defect in planetary bevel gear differentials has long been recognized, it has heretofore beendeemed diflicult, if not commercially impractical, to devise a power transmission and differentiating mechanism free from the stated disadvantage. In some proposals, it has been suggested that recourse be had to an irreversible worm or worm wheel as elements of .the mechanism, to insure the transmission of power to both driven axles. Such power transmission as may be thusobtained, however, is at the expense of-freedifferentiation, with the result that such wo'rm gears tend to grind against each other under conditions of use, thus leading to mutual self destruction and failure in practice.

Without entering here upon an exhaustive discussion of the mechanics of bevel gear differentials, or those depending upon an arbitrarily cut irreversible worm, it may be said of the first type "latter case, power extent that free differential movement is sacrisolve the problem that good differentiation is obtained at the expense of eflicient power transmission, while in the transmission is achieved to the ficed. These two eflects, in mechanisms heretofore proposed as known to me, have thus been opposed to each other, and attempts made to by a compromise of properties have resulted in practical failure, both because of the conflict of forces and the great difliculty o encountered in making, on aeconomical basis, physical structures which satisfy the. comprise theory.

According to the present invention, it is proposed to provide a worm and worm wheel combination, which, under certain conditions of operation, will act as an ordinary irreversible worm gearjthereby permitting the efllcient transmission of power, and, under other operating conditions, will act as a reversible worm gear, 20 thereby permitting free differential movement. Stating .the matter in other words, the invention proposes the selective utilization of a irreversible and a reversible worm, depending upon the need for power transmission or diiferentiationo It may be stated here that, in the ordinary form of worm and worm wheel, the helix angle of the worm thread is such that, if the worm is rotated in either direction, a corresponding motion of rotation will be imparted to the worm 3 wheel, but, if an attempt is made to drive the wheel to effect the rotation of the worm, it will be found that the thread and teeth jam against each other, and no rotary motion 'will result. This effect is referred to as the irreversibility of the worm. On the other hand, the helix angle of the worm may be greatly increased so that rotary efiort applied to the wheel in either direction will cause a rotary motion of the worm, in which case the wonn is said to be reversible. In the present invention, there is provided a worm and worm wheel,-in which the thread and teeth contact with each other in varying relationships under different conditions of operation, with the result that rotary effort applied to the worm in either direction will cause a corresponding rotary motion of the wheel, and rotary effort applied. to the wheel in one direction will cause the gearing to behave as irreversible gearing, while rotary 5o tion of rotary motion, I regard as new with me,

- through an irreversible worm -gearing,with the In applying the principle of selective reversibility to an power transmission and diiferential gearing, the parts are so arranged that under normal operating conditions when differentiation is not' required, power is transmitted to the driven shafts result that the automobile, for example, will be positively driven forward even though one wheel is on ice, or in mud, or is even free from the ground. On the other hand, if the car is turning a corner, so that differential motion is required between the driven wheels, the contact on one side of the car, or to one wheel, is made through a reversible gearing, whereby such wheel may rotate at a different speed than the other. Such differential mechanism I also regard as my invention, whether the same incorporates the specific form of worm and worm wheel hereinafterdescribed, or whether used on an automobile or in other relationship. From a consideration of'the hereinafter described embodiment of the invention, it will be noted that there is further provided various new and improved instrumentalities in gearing, all of which are intended to be madethe subject of the appended claims.

In the drawings: Fig. 1 is a longitudinal section of a differential mechanism for an automobile, the view being taken'from the upper side of the vehicle;

Fig. 2 is a transverse section on the line 2-2 of Fig. 1, or looking to the left driven wheel;

Figs. 3 and 4 are fragmentary sections of a worm and worm wheel on an, enlarged scale,

showing the contact of the thread and teeth under different conditions of operation, such as forward linear movement and while turning a corner; and,

Fig. 5 is a plan view of the worm, with various legends applied thereto to show the nature of the thread.

The invention as applied to an automobile differential is shown in Figs. 1 and 2, in which a typical form of rear housing is indicated by the reference numeral in, into which extend the drive I shaft II and the left and right rear or driven axles l2 and it, which carry the driven wheels, not shown. The drive shaft II is mounted in the housing It by means of a roller bearing l4, while the axles l2 and II are supported in part by the ball bearings II and I, through the medium of acarrier' II.

- The carrier I1 is formed of two similar sectionsit and Is, the left hand section it being formed with a flange 2|, to which is secured a ring gear 22, adapted to mesh with a driving pinion 23 secured to the end of the drive shaft H. The carrier section it is also formed with a centrally p sed hub 24 which is rotatably mounted in the bearing II. The right hand section II islikewise formed with a hub 25, rotatably molmted in the hearing it, and also with a" radial portion 26..

Both sections it and it are formed with inwardly extending lugs 21 and II, respectively, adapted to abut each other, and pierced to receive through that, as the drive shaft is rotated, the carrier 11 isrotatedinitsbearings and I6.

'lhecarrierlflformsahousingfortheendsof' the driven axles l2 and which project within the interior thereof. Worm wheels. and 2 are fused.

I: by means of splineconnections 33, and each wheel is formed with a hub portion '34 or 35 adapted to be positioned between the axle and the adjacent portion of the housing I! to form radial and end thrust bearings, which are brought 6 into play as occasion requires. From a consideration of the operation, as hereinafter set forth,

it will be apparent that these bearings need not be elaborate, as under most conditions there is little or 'no relative rotation between the housl0 ing sections l8 and I9 and the hubs 34 and 35.

- The driving connection between the rotating carrier l1 and the worm wheels 3i and 32 is provided by a plurality of worms 31, which are mounted on brackets 38 and 38, formed integral 15 with and projecting inwardly from the radial portions of the sections l8 and it. As best shown in Fig. 2, three brackets are formed on each section, and they are adapted to abut each other and to be secured by means of through bolts 4|. 20'

Each of the brackets II and I9 is formed with angularly related sections 42 and 43, so arranged that adjacent portions of each pair of brackets are parallel to each other, and so spaced as to provide amounting for the worms. In the spe- 25 ciiic embodiment herein shown, there are three sets of brackets on each housing section, to-provide mountings for three worms, but it will be understood that a greater or less number may be Each of the worms :1 is formed at its efids with a spur gear 45, which is adapted to mesh with the aligned spur gear of the opposed worni, as shown in Fig. 1. Each worm is also formed with an ax- .ial bore 46 terminating, at one end, in a cylindrical recess 41, which is also in communication with a radial bore 48, and at the opposite end in a conical recess 49, communicating with a radial bore ii. The various passagesare provided to permit the flow of lubricant, the intermeshing spur gears serving asa pump to force lubricant around the bearing recesses 41 and.

As best shown in Fig. 2, the opposed bracket portions 42 and 43 are formed with axially aligned and tapped holeswhich receive the threaded 45 shanks of bearing pins it and 54, each of which is formed on its outer end with a perforated head 55, which receives a tie wire it extending to a like perforation of anadjoining bearing pin. The

tie wires serve to secure .the bearing members in a fixed position, after the mechanism has been properly assembled. The sections 42 of the brackets' 38 and 39, which are disposed adjacent the cylindrically recessed ends 41 of the worms,

are also formed on their inner faces with pads 31, thereby providing both a radial and a thrust bearing. It will be noted that the inner portions of the hearing pins are also formed with ducts to permit the e of lubricant at all times. with this construction, the worms 3'! are tangentially mounted with respect to the worm wheels II and II, and they may beaddusted axially through the pins 4 to provide uniform bearin: contact. I

The detailed formation of the thread of the worms 3! is best shown in Figs. 3, .4, and 5, from which it will be noted that the contact between 'the worm thread andthe wheel teethis such as to produce an irreversible effect under certain .7

conditions, and a. reversible effect under other conditions. v

Referring first to Fig. 5, it will be observed that the worm is formed with a single thread having a critical relationship between its lead and inner.

above described, the cross-sectional shape of the worm thread is also changed from the conventional in thatone side of the outer or adden- I dum portion of the thread is relieved (or, what is equivalent, the root portion is'built up), so that, in section, the worm appears as shown in Figs. 3 and 4. Thus, in Fig. 3 it will be seen that one face of the worm 6| is symmetrical with the root portion 63 of the opposite face of the thread, but is not symmetrical with the opposite addendum portion 62, which is relieved.

Thev teeth of the worm wheel 31 or 32 are also deformed from the customary involute or other shape, so that, while the tooth on one face 64 is symmetrical at all points with the dedendum portion 65 of the opposite face, it is not symmetrical with the opposed addendum portion 66, which is relieved. It will thus be seen that, when the worm wheel is rotated in one direction, as, for example, counter-clockwise, the teeth of the wheel engage the thread of the worm on the outer portion only of the worm thread, and this 'drive is accordingly irreversible. When, however,

the worm wheel is rotated in a clockwise direction, the wheel teeth engage only the root or reversible portion of the worm, and rotation of the worm can thereby be effected: When the worm -is made the driving member, driving contact is obtained either at the addendum or dedendum portions of the wheel teeth, depending upon the direction of rotation, but in both cases, the wheel is constrained to rotate.

Considered from a structural viewpoint, it will be apparent that the principle of selective reversibility embodied in the gearing illustrated may be utilized by relieving both sides of the teeth of the wheel, or both sides of the thread, without deforming the remaining member, but the form disclosed is preferred because of considerations of cost and facility of manufacture with present day gear cutting practice. Likewise, it will be understood that single or multiple thread worms may be used, or a part of the worm may be made fully reversible, with the remaining portion irreversible, for contact with a pair of wheels. These variations, however, the invention,

the form illustrated is deemed by me to represent a satisfactory and practical embodiment of the invention.

From a consideration of the nature of the gearing, it will also be apparent that there is provided a ratchet type of mechanism wherein, during motion in one direction of the worm wheel, rotary movement is imparted to the worm, while motion of the wheel in the opposite direction does not produce rotary movement of the worm on its own axis, but necessitates movement of the worm along with the wheel.

Considering the operation of the mechanism shown in Figs. 1 and 2 in conjunction with the foregoing explanation of the gearing, it will now.

. through the gearsil driving, and

' portion of the the same rate of speed, 'wheel from the pavement, or change in resistance,

of the other'wheel, or

while within the purview of need not be discussed further, as

attempted motion of "are all proportional, as is be understood that. as the drive shaft II is rotated, the housing I! is caused to rotate, and 22. In forward linear assuming substantially equal loads on the two axles l2 and IS, the clockwise rotation of the housing l1 causes the worms 31 and wheels 3| and 32 to contact in the manner shown in Fig. 3, wherein the addendum or irreversible worm dendum portions of the gear teeth. Any tendency of the worms to rotate is opposed by the intermeshing of the spur gears 45, and which would,

threads engage the deunder the conditions assumed, have opposed rotarytendencies when regarded as driving or driven gears. As a net result, the worm wheels 3| and 32 are pulled around with the carrier l1, and the vehicle is therefore driven forward in a positive manner.

If it next be assumed that one of the driven wheels, during such forward movement, encounters sand, mud, ice, or like slippery material, it will be understood that no change is effected in the driving conditions through the gearing. Each wheel is still pulled around at and the freeing of either does not cause the freed wheel to spin ahead impede driving through such wheel.

If-the car is now driven in reverse, the, contact between the threads of the worms and the teeth of the wheels will be changed from the position indicated in Fig. 3 to that shown in Fig. 4. However, positive driving eflort is imparted to both wheels, since any tendency of one wheel or the other to move at a different rate than the opposite wheel is oflfset by the reaction on the opposite wheel through the spur gears 65.

Considering next a movement of the car in a curved path, during which differential movement between the rear axles i2 and i3 is required,

it will be understood that the contact between worms and wheel will be as shown in Fig. 3, for one side of the mechanism, and as shown in Fig. 4 for the opposite side. It will be assumed, in this case, that the car so that the mile 82 represents the axle for the inside wheel a for the outside wheel, which must move through a longer radius. The worm wheel ii is thus driven, the contact being as shown in Fig. 3. The outer worm wheel 82, however, must move through a greater distance, and hence it moves ahead of its worms, taking the position shown in Fig. 4, which is the position for reversible'driving through the worm wheel to the worms. The right hand worms may therefore rotate slowly on their axes, thereby causing a counter-clockwise movement of their associated spur gears. tion of movement, however; is not opposed to the the spur gears 4.5 of the left hand worms, which is clockwise, and hence the spur gears 45 of the left hand worms may rotate to any required extent, causing a partial release of the connection between such worms and the left hand worm wheel 3|. This motion, in effect, slightly reduces the rate or movement of the inside wheel, but the variations in motion the principle as applied to automobile diflerential mechanisms provides for a positive Such direcrequired in efiective 7c drive at all 75 following claims.

times, and one in which free'diiferentiation may be obtained as occasion requires, without concurrently causing undue wear on the engaging gears..

While the invention has been set forth with reference to one specific form of worm. and worm wheel, and one particular application thereof, it will be understood that it is not intended thereby to limit the invention, the scope of which should be determined from Iclaim: I

1. A worm and worm wheel gearing compris- 'ing a worm having a thread formed thereon, the helix angle at the outer portion of said thread being irreversible and the helix angle at the inner portion of the thread being reversible, a worm wheel formed with a plurality of teeth adapted to engage. said thread during relative ing a worm wheel formed with a thread having an irreversible-helix angle adjacent its outer portion and a reversible helix angle adjacent its inner portion, and a worm wheel formed with a plurality of teeth adapted to engage said thread upon rotative movement, said thread and teeth being relatively formed with relieved portions adjacent their outer extremities on a common side, whereby the teeth will engage the outerportion or the inner portion only of the thread in accordance with the relative direction of rotation of the wheel with respect to its axis.

3. 'In a differential mechanism, a pair of axle sections each having a worm gear secured thereto, a drive shaft, a worm carrier, means connecting the carrier ifor operation by the drive shaft, worm means mounted on said carrier comprising a worm meshing with each worm gear,

said worms being both formed with a similar thread, said thread being relieved on one side to provide a dedendum surface contact withthe worm gear and the gear teeth being relieved to provide the contact of the addendum surface of the thread therewith on the opposite side of the thread, said addendum surfaces each having an irreversible helix angle and being adapted to engage the gear teeth to rotate their respective driven shafts, said gears when engaging the worms in a driving action being adapted to engage the dedendum surfaces thereof to cause rotation of their respective worms, and means gearing the worms to each other.

4. A power transmission device comprising a worm gear and a worm mounted in meshing engagement therewith, said worm being formed with a thread having one side partially relieved to provide a dedendum surface contact with the worm gear, the gear teeth being relieved on one side to provide for contact thereof with the the import of the ing the carrier for operation by the drive shaft,

worm-means mounted on said carrier comprising a worm meshing with each worm gear, the teeth of each worm gear and the thread of its. respective worm being mutually formed to provide contact of the teeth with a peripheral face of the thread when the worm is in forward driving engagement with the gear, and the contact of the 20 teeth with a root face of the thread when the gear is in forward driving engagement with the worm, said peripheral face of the wormthread having a non-reversible helix angle and the root face of the thread having a reversible helix angle, 25 and means gearing the worms to each other.

6. A power transmission device comprising a worm gear and a plurality of worms meshing therewith, a carrier for mounting said worms for planetary movement about said worm gear, a plurality of pairs of bearing supports on said carrier, each pair adapted to receive a worm therebetween, an axial conical bearing surface formed at one end of each worm, and a bearing adjustably mounted in each support and having a coni- 35 cal surface engaging in'the conical bearing surface of a worm. i V

7. A power transmission device comprising a worm gear and a plurality of worms mounted in meshing engagement therewith, the teeth of said 40 helix angle, means for mounting said worms in spaced relation about said gear, and adjustable bearing'means for adjusting the axial position of each worm to obtain simultaneous contact of the worms with the gear.

8. A power transmission device comprising a worm gear and a worm mounted in meshing engagement therewith, the teeth of said worm gear and the thread of said worm being mutually formed to provide contact of the teeth with a peripheral face of the thread in one direction of movement and the contact of the teeth with a 00 root face of the thread in the opposite direction of movement, said peripheral face of the thread having a non-reversible helix angle and the root face of the thread having a reversible helix angle.

roam sl MORGAN. 

